n, plgas*esalsogas*ses 1 : a fluid (as air) that has neither independent shape nor volume but tends to expand indefinitely 2 : a gaseous product of digestion : also : discomfort from this 3 : a gas or gaseous mixture used to produce anesthesia 4 : a substance that can be used to produce a poisonous, asphyxiating, or irritant atmosphere vt, gassedgas*sing 1 : to treat chemically with gas 2 : to poison or otherwise affect adversely with gas .abbr general adaptation syndrome .